The accuracy requirements for processing machines have risen continuously in recent years. Against this background, machine measurement is now of major importance. This relates both to machine measurement when setting up the processing machine and to regular monitoring of the machine accuracy throughout the entire life of the processing machine.
Numerous methods have been disclosed for machine measurement (Textbook “Werkzeugmaschinen—Meβtechnische Untersuchung und Beurteilung”, [Machine tools—measurement investigation and assessment], Manfred Weck, 6th Edition, 2001, Springer-Press, Chapter 3 “Geometrisches und kinematisches Verhalten von Werkzeugmaschinen”) ([Geometric and Kinematic behaviour of machine tools]).
A major proportion of the known methods are based on the use of laser interferometers for determination of positioning discrepancies, linearity discrepancies, angular discrepancies, or the like.
The known method for machine measurement (WO 2009/030585 A1), on which the invention is based, discloses a vertical processing machine having a permanently installed laser beam generator, whose measurement beam passes through the spindle unit. For this purpose, the spindle is in the form of a hollow spindle, thus allowing the measurement beam to pass through the spindle, for machine measurement.
Beam detectors are provided separately from the single beam generator, and are fixed to the machine bed or to the machine table.
Both the beam generator and the beam detectors are permanently installed in the processing machine. In principle, this makes it possible to carry out an automated machine measurement without having to manually set up any measurement fittings.
The known method is intended for a three-axis vertical machine, as a result of which the measurement beam is always vertical. In order to carry out measurements on the horizontal, work must be carried out with a direction-changing mirror, which can be substituted via the tool interface. In this case, it has been found that the measurement tasks which can be carried out using the known method are restricted. By way of example, additional beam detectors have to be used for a volumetric measurement with the normal diagonal measurement. This leads to a costly, high-maintenance arrangement.
Finally, the known method has the disadvantage that the permanently installed laser beam generator is always subject to the working area constraints, some of which are severe. A major maintenance effort can also be expected here, because of vibration, dirt and moisture.
For the sake of completeness, it should also be noted that a so-called laser tracker is known for machine measurement. A laser tracker such as this is equipped with a laser interferometer, which is arranged on a support. In order to position the laser interferometer, the support has two NC pivoting axes which are arranged at right angles to one another. A suitable sensor arrangement allows the laser interferometer to be slaved to a reflector which is inserted into the tool holder on a processing machine. The absolute position of the machine head of the processing machine can be determined very accurately from the measured distances and the respectively inserted pivot angles. The high level of hardware complexity is disadvantageous, in particular with respect to the two additional NC pivoting axes.